Evidence for cleft palate as a postfusion phenomenon.

Some clefts of the lip and palate appear to result from the rupture after fusion has occurred. This possibility is suggested by (1) epithelial remnants found in the palatal shelves, (2) regenerating epithelium found in the palatal clefts of human fetuses older than 13 weeks, (3) immature epithelium visible on the margin of the cleft, (4) nasopalatine ducts cut off by clefts, (5) perforation type cleft found in the hard palate, (6) a Simonart band visible in six cleft mouse fetuses, (7) duplicated upper lateral incisors enclosing a lip-jaw cleft, and (8) rodent cavities in the lip or palate related to cleft formation.